The Black Hole Mass Distribution in the Galaxy

Abstract

We use dynamical mass measurements of 16 black holes in transient low-mass X-ray binaries to infer the stellar black hole mass distribution in the parent population. We find that the observations are best described by a narrow mass distribution at 7.8±1.2 M . We identify a selection effect related to the choice of targets for optical follow-ups that results in a flux-limited sample. We demonstrate, however, that this selection effect does not introduce a bias in the observed distribution and cannot explain the absence of black holes in the 2-5 M mass range. On the high-mass end, we argue that the rapid decline in the inferred distribution may be the result of the particular evolutionary channel followed by low-mass X-ray binaries. This is consistent with the presence of high-mass black holes in the persistent, high-mass X-ray binary sources. If the paucity of low-mass black holes is caused by a sudden decrease of the supernova explosion energy with increasing progenitor mass, this would have observable implications for ongoing transient surveys that target core-collapse supernovae. Our results also have significant implications for the calculation of event rates from the coalescence of black hole binaries for gravitational wave detectors.

The Fate of the Compact Remnant in Neutron Star Mergers

“…The explosion occurs within the first 0.1-0.2 s driven by a convection and neutrino enhanced engine. This "rapid" supernova engine reproduces ) the observed mass gap (apparent lack of neutron stars and black holes with mass in range 2-5 M e ) in Galactic X-ray binaries (Bailyn et al 1998;Özel et al 2010). Additionally, we include NS star formation through electron capture supernovae (ECS) for low mass progenitors M zams ∼ 7-11 M e .…”

“…For a non-spinning BH this occurs already near M BH = 8 M ,  so that BHs of the masses that are thought (Belczynski et al 2008b;Özel et al 2010) to be most likely (∼10 M  ) need large dimensionless spin parameters, a 0.9, BH  to form sizeable disks (Foucart 2012). Finally, the inclination of vector of BH-NS orbital angular momentum to BH spin vector plays an important role in the formation of a torus.…”

The Mass Function of GX 339–4 from Spectroscopic Observations of Its Donor Star*

“…Although a low system inclination would still allow for a BH more massive than 5 M e , the mass function of GX 339−4 is much lower than has been assumed to date and it may in fact be the first BH to fall in the "mass-gap" of 2-5 M e (Özel et al 2010;Farr et al 2011). …”

On the Mass Distribution and Birth Masses of Neutron Stars

“…We summarize the neutron star mass measurements and their uncertainties in each subgroup in Figure 13 and compare them to those of black holes in Figure 14 (compiled and analyzed in Ozel et al 2010a). In these figures, the error bars correspond to a 68% confidence level calculated from the detailed likelihood distribution presented for each subgroup of sources in Section 2.…”